Impactless printer

ABSTRACT

An impactless printer and control having movable heads with stylii extending therefrom for marking a coated paper. A stepping motor is used to transmit motion to the head so that the printer is asynchronous. Gating means control the output of a memory device connected to input data lines. The gating means are responsive to and actuated by a strobe pulse which controls the timing operation of the device.

iJnited States Patent Drapeau Oct. 24, 1972 [54] IMPACTLESS PRINTER 3,476,877 11/ 1969 Perkins ..l78/30 [72] inventor: RaoulEDraPeauViennaVa 3,488,664 1/1970 Winston ..178/30 [73] Assignee: Scope Incorporated, Reston, Va. Primary Examiner-Kathleen H. Claffy Assistant ExaminerWilliam A. Heivestine [22] Filed. Feb. 13, 1970 Atmmey John E. Benoit [21] Appl. No: 11,147

[57] ABSTRACT [52] U.S,Cl ..178/30 An p fl s p nt and ntrol having movable 51] Int. Cl. .11041 15/24,11041 15/ 34,11041 17/16 heads with stylii extending therefrom for marking a [58] Field of Search ..l78/30 coated paper- A pp g motor is used to transmit motion to the head so that the printer is asynchronous. [56] References Cited Gating means control the output of a memory device connected to input data lines. The gating means are UNITED STATES PATENTS responsive to and actuated by a strobe pulse which d 3,512,158 5/1970 Scarbrough ..l78/30 commls the pera ofthe evce 3,419,887 12/1968 Moran ..178/30 5 Claims, 9 Drawing Figures ASTABLE (VAR BISTABLE HlGH VOLTAGE M BIT RING CTR READ-ONLY 1421mm TO PRINTING ELEMENTS P'A'TENIEnum24 m2 3700.807

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I sum 5 or 5 INVENTOR.

RAOUL E. DRAPEAU IMPACTLESS PRINTER The present invention relates generally to page printers and more specifically to an asynchronous impactless page printer.

Impactless page printers are a useful solution to the problemof rapid printing of alphanumeric information without going to the expense of a line printer or other similar device. This type of irnpactless printer uses a coated paper which has the property wherein a voltage applied to a stylus resting on the surface thereof causes a mark to be made at that point. A collection of such dots forms the character. The device uses a linear column array which is energized as many separate times as there are columns of data in the character (typically The printer of the present invention has been made asynchronous such that any number of characters may be printed sequentially followed by any arbitrary delay. That is, the characters need not be printed at a fixed rate. This type of operation is achieved through the use of a stepping motor which moves a specific, unchanging amount for each character. This motion may be translated into the proper linear motion through a belt and pulley arrangement with the printing heads being transported by the belt.

The use of a printing head which serves to carry electrical impulses from a commutator to the printing site is known. The present device however, incorporates a number of improvements over previous embodiments, especially in the electrical area and in certain mechanical aspects, such as the ability to see the printing without it being covered by the head.

Accordingly, it is an object of the present invention to provide an asynchronous irnpactless page printer.

A further object of this invention is to provide an asynchronous irnpactless page printer wherein the printing is continuously visible.

A still further object of this invention is to provide an improved electrical control system for providing the input signals to the printing head of an asynchronous irnpactless page printer.

These and other objects of the invention will be more clearly understood from the following description taken together with the drawings wherein FIG. 1 is an illustrative example of a character as printed by the device of the present invention;

FIG. 2 is an elevation view of the driving arrangement for the printing heads and paper feeding device;

FIG. 3 is a plan view of the drive mechanism for the printing heads;

FIG. 4 is a partial view of the belt and one printing head attached thereto;

FIG. 5 is a side view of the paper storage and feeding apparatus;

FIG. 6 is a schematic diagram of the electronic system for supplying signals to the printing elements;

FIG. 7 is an illustrative timing diagram for the system of FIG. 6;

FIG. 8 is a schematic diagram of a high voltage pulse circuit, and

FIG. 9 is a schematic diagram of a motor stepper circuit used with the present invention.

Turning now more specifically to the drawings, FIG. 1 shows a typical print of a letter A wherein there are N rows, one per individual stylus, and M columns. The number of columns and rows is typically 5 X 7, but may assume on any other applicable combination.

Referring now to FIGS. 2 through 5, the mechanical system of the printer will be discussed.

Print heads 18, 19 and 20 are carried by the belt, and the high voltage pulses are translated to the printing stylii 22 by means of contactor leads 24 adjacent to a commutator 28. That is, wires 23 (FIG. 4) imbedded in the head 19 electrically connect the printing stylii 22 and the contactor leads 24.

It should be noted that the number of heads used is dependent upon the particular application involved. The printing heads l8, l9 and 20 are designed so that they permit full view of the character as it is printed that is, the character is not covered up by the head or belt in any way. Stepper motor 11 drives pulley 13 and hence belt 15. Drive roller 39 is driven in turn directly from motor 11 through a worm and gear 31, shaft 29 and drive belt 33. Because the paper advance is directly linked to the motor, there is no need for a separate paper advance arrangement. Thus, in the interval between the positioning of two successive heads, such as 19 and 20, the paper has moved upward by an amount equal to the desired inter-line spacing.

The rollers connected by shaft 41 maintain contact pressure between paper 26 and drive roller 39. These rollers are mounted on the frame (not shown) by arms 42.

Since the paper 26 moves up between the continuous belt 15, the system takes up less space than if the belt were entirely in front of the paper.

A pressure plate 25 is mounted in front of the head so as to supply positional accuracy to the head and insure an even printing pressure regardless of the position of the head in its travel as shown more clearly in FIG. 3. Further, the point of attachment of the head 18 to the tape 15 by means such as rivets 21 is at the tailing edge of the head as shown in FIG. 4. This positioning permits the belt itself to provide much of the opposing force which counters the forces from the printing stylii and commutator contactors. The pressure plate 25 prevents the head from being displaced too far away from a direction of travel parallel with the platen 51; since the tape alone is unable to supply all the required force to maintain firm contact as the head is moved.

The mechanism which supports and feeds the paper is illustrated in FIG. 5. It has been designed for ease and safety of loading, and functions as follows. Plate 47 is secured to the frame (not shown) by pin 49 and pivots thereabout so that it may be moved outwardly, as shown in the dotted lines, to insert roll 43. When pivoted out, an interlock (not shown) removes power from the machine. Plate holder 47 is then outside the machine, which permits a safe and convenient loading. The roll 43 simply clips into place in a known manner, and, by merely unwinding the roll, the paper follows a path between two curved plates 51 and 52. Roller 41 is mounted by arms 42 on a pivot connected to the frame (not shown) and lifts to permit passing the paper between it and roll 39. When the paper is completely threaded, roll 41 is released and the paper is gripped between rolls 41 and 39. The roll holder 47 may now be pivoted back thereby fully enclosing the paper within the machine. The paper center of gravity which would be located along roller 50 is inside the pivot point 49 so that no separate catch is necessary.

FIGS. 6 and 7 show block and timing diagrams relating to the electronic control circuitry for the printer.

One of the primary advantages provided by this circuit is the relative simplicity thereof. Consequently, the overall electronics includes relatively few components and the mechanics include relatively few moving parts.

The control system of FIG. 6 is actuated by a strobe pulse which'causes the input latch 51 to hold the state of the input data lines at the time of the strobe. These data lines are encoded in some character code, such as ASCII (not shown). Latch 51 serves as a buffer so that once the printing process is initiated, the input lines may change without affecting operation. These latched data lines then address the read-only 'memory character-generator 55 which has connected thereto a number of column enable lines 57. In operation, these column enable lines are turnedon one at a time in sequence by a multi-stage ring counter 59 or similar circuit. Each column when enabled provides at the output lines 60 a number of row signals, in this case seven. For example, referring to FIG. 1, for the second column, these signals would be (counting down), 1,0,0,l,0, 0,0. It is this succession of row signals which is the control for printing a matrix character, columnby-column. That is, a matrix-organized character consists of M columns of N rows each. The printing process involves passing a linear printing head array having N stylii across the paper and energizing it M separate times with the information appearing at the output lines 60.

The strobe, in addition to latching the character code bits, initiates a time delay circuit 61. It is only after this delay that printing is possible. The purpose of the delay is that, due to inertia, the drive motor 11 does not attain full operation speed immediately. Consequently, the delay disables printing during the acceleration period since printing should occur during a time' of approximately constant motor velocity. The delayed strobesets the bistable 63, allowing the output from astable 65 to be gated through gate 67, which signal drives the M-bit ring counter 59 and the high-voltage pulse supply 69. After M astable pulses have passed, the bistable 63is reset thereby preventing any further pulses from reaching the ring counter 59 or the high voltage supply 69. The ring counter is present once each character cycle to insure that it always starts in the right phase (all stages a logical zero except for the first). This presetting can be done by the variable delay as shown. The M pulses from astable 65 are also the drive for the high voltage pulse supply described elsewhere. The timing of these high voltage pulses is given in the system timing diagram FIG. 7.

For purposes .of illustration, the various locations of interest are noted with alphabetical characters. These pulses are introduced to the high voltage gates 70 whose purpose is to pass the pulse or not depending on the state of the particular row line at that time. If the row line is a logical 1," then output 71 for that particular line rises to the voltage required for printing.

The rate of the pulses from astable 65 is variable to account for various mechanical loads and motor torques. This capability permits the print pulse rate to be matched to the slope of the motor velocity curve. Thus, the stepper motor 1 1 which moves a fixed increment with each strobe pulse and in turn drives the print head can have its travel divided into approximately M-l-l equal distance increments (M+l increments allows for an inter-character space). It is because the motor moves with a reasonably constant velocity after initial acceleration, that the fixed period astable pulses can perform this function satisfactorily.

The astable pulses may be synchronized to the end of the delay as shown to provide repeatability, but this is not necessary.

There is a mode, usually called carriage return, during which the movement of the printing head is essentially continuous and usually occurs at a rapid rate. This rate continues until the next head is in position to start the next line. The mechanism which disconnects the motor from the carriage return mode and stop is a control line 73 which is actuated by a shorting loop 71 integral to the print head (FIG. 4). Thus, when the head passes by the point on the commutator where the control line is located, the control line is grounded, thereby stopping the motor.

Referring to FIG. 8, this circuit is a simple means of providing high voltage pulses on command from a low voltage control circuit. This circuit is indicated as high voltage supply 69 in FIG. 6. These pulses are used to supply the printing energy in the stylii which create the marks on the paper.

The circuit operation is as follows:

Normally, the input to inverter 75 is low 0 volts) which makes the output high +5 volts). Consequently, transistor 01 is kept off and transistor Q is saturated. Because transistor Q effectively shorts the output to ground, there is essentially no output at V as indicated by the dotted line. The voltage across the power supply capacitor C is unaffected because Q, is off and there is not a closed path through which current could flow.

When the input to inverter 75 goes high and its output goes low (less than the indicated 2 volts on the emitters), transistor Q is turned ofi since its base is at a lower potential than its emitter. At the same time, transistor Q becomes saturated which effectively grounds the negative side of capacitor C. As a result, V rises to nearly the full potential across capacitor C, (less about 2 volts) as shown by the solid pulse line output. Since transistor O is held off, it does not interfere with the output rise.

While a positive pulse circuit is shown here, negative voltage pulses could be produced by reversing capacitor C, the input pulse, and the roles of transistors Q, and Q Transistor Q is not necessary for circuit operation, but it does insure that V does not rise above ground due to leakage currents. It could be replaced by a resistor from the output point to ground.

Referring to FIG. 9, the two phase type of stepper motor used in the present invention has the characteristic that the direction of rotation is determined by the sequence of applied voltage on the four windings M M and N N Consequently, it is necessary to insure either that the sequence never changes or that if it does, that fact is detected and an appropriate correction is made. Because the former is difficult, the latter approach is used here.

The motor requirements are such that one coil in each of the two pairs should always be energized. Thus,

controlling the coil pairs from a binary is a logical step.

Here, binary A2 controls coil pair M and A3 controls pair N. Both A and A are controlled by the drive binary Al. For each input strobe, A1 changes state.

E: Q1$( QfiQs) Eq. (1) where 9 refers to the exclusive or logical operation.

TABLE I. FORWARD MOTOR SEQUENCE Position Q Q Q 1 l l l 2 0 0 l 3 l 0 0 4 0 l 0 The four positions in Table I are called valid forward conditions, because if the three binaries are in any of the four combinations of states shown, then the next pulse applied to Q will cause a forward step such that the new combination of binary states corresponds to that in the next lower row.

The motor can be made to operate in the reverse direction by making the binaries assume the states shown in Table II. Note that whenever one of the binaries is a logical 0, the other two are the same as each other, and whenever one of the binaries is a logical l the other two are different from each other. It can be shown that this-agrees with the logical equation:

TABLE II. REVERSE MOTOR SEQUENCE Position Q, Q, Q;

l l l 0 2 0 0 0 3 1 0 l 4 0 l 1 The four positions in Table II are called valid reverse conditions.

The motor error sensing circuits for the forward direction are implemented by performing the exclusive or operation indicated in Eq. 1. Because Eq. 1 is associative this can be implemented by taking a logical exclusive or on any two of the three binary outputs, then performing a logical exclusive or between that and the third output. If the logical inputs to the motor error sensing circuits correspond to any one of the four positions shown in Table I, no Error Correction Signal is generated at the output of the motor error sensing circuits. If the logical inputs to the motor error sensing circuits correspond to any one of the four positions shown in Table II, the motor is attempting to operate in the reverse direction and an error correcting signal is generated. This signal is then used to reset the binaries to any one of the four valid forward states in Table I. Succeeding pulses will then cause the motor to run in the forward direction. An implementation of this error-correction logic is shown in FIG. 9. The two ex elusive or elements can be a self-contained integrated circuit such as Texas Instruments SN7486, or they can be constructed from more logical gates.

Since Eq. 2 is the complement of Eq. 1, the motor error sensing circuits for the reverse direction are implemented by complementing the output of the exclusive or arrangement in FIG. 9 and connecting the preset inputs of the binaries to any of the valid reverse conditions as shown in Table I]. Then, if the logical inputs to the motor error sensing circuits correspond to any of the four positions shown in Table II, no error signal is generated. If the logical inputs to the motor error sensing circuits correspond to any of the four positions shown in Table I, an error signal is generated and the binaries can be preset to any one of the four valid reverse positions as shown in Table II which restores reverse direction operation. v

The R -C combination provides a slight integration so that normal switching transients do not activate the correction function.

The transistors T through T, provide a buffer so that the motor coil current does not flow through the logic elements.

The resistors R and R are present to make the circuit more closely approximate a constant-current motor supply. This procedure improves operation because of the fact that while stepping, the permanent magnet rotor induces a back emf which tends to decrease motor coil current if a constant voltage source is used. With a constant current source, this effect is reduced and the motor performance is improved.

It is to be understood that the above description and accompanying drawings are to be considered as illustrative only since individual components could be substituted without departing from the scope of the invention as defined by the following claims.

I claim:

1. In an impactless, asynchronous teleprinter for printing characters in a matrix font including a printing stylii head having a plurality of electrodes and movably carried by a belt transversely of a recording sheet, a printing control comprising input circuit means for receiving a trigger pulse,

input latch means coupled to said input circuit means,

circuit means for coupling input data row lines to said latch means and supplying coded impulse signals to said latch means,

read-only memory character generating means coupled to the output of said input latch means,

high voltage gates coupled to the output of said character generating means,

variable delay means coupled to said input circuit means,

bistable means coupled to the output of said variable delay means,

variable rate astable means coupled to the output of said variable delay means,

gating means responsive to the outputs of said astable and bistable means,

a ring counter coupled to the output of said gating means,

a plurality of column enable lines coupling said ring counter to said character generating means, said ring counter sequentially energizing said enable lines,

a plurality of high voltage gates equal in number to said plurality of electrodes coupled to the output of said character generating means, said gates receiving signals responsive to coded signals supplied to said memory character generating means by said input data row lines,

high voltage pulse supply means gated by said gating means,

means coupling said high voltage'supply means to said high voltage gates,

circuit means for coupling the outputs of said high voltage gates to said electrodes in said printing head,

circuit means for coupling said bistable means and said input latch means to said ring counter whereby said bistable means and said input latch means are reset at the termination of said counter sequence, and

motor means coupled to said input circuit means for driving said belt and moving said recording sheet in response to said trigger pulse.

2. The teleprinter of claim 1 further comprising switch means integral with said printing stylii head for controlling said motor so as to position said head.

3. The teleprinter of claim 1 wherein said head comprises a plurality of insulated electrode fingers extending transversely from said head whereby said printing is visible as it is being printed. 4. In an irnpactless, asynchronous teleprinter for printing characters in a matrix font including a printing stylii having a plurality of electrodes and movably carried by a belt transversely of a recording sheet, a printing control comprising input circuit means for receiving a trigger pulse, input data lines for supplying coded signals representing the character to be printed, character generating means coupled to said input data lines, gating means coupled to the output of said character generating means, bistable means coupled to said input circuit means, variable rate astable means coupled to said input circuit means, said bistable means and said variable rate astable means supplying a sequence of pulses in response to said trigger pulse, enabling means coupling said bistable means and said variable rate astable means to said character generating means, and circuit means for coupling said gating means to said input circuit means. 5. The printing control of claim 4 further comprising variable delay means coupled between said input circuit means and said bistable means and said astable means. 

1. In an impactless, asynchronous teleprinter for printing chAracters in a matrix font including a printing stylii head having a plurality of electrodes and movably carried by a belt transversely of a recording sheet, a printing control comprising input circuit means for receiving a trigger pulse, input latch means coupled to said input circuit means, circuit means for coupling input data row lines to said latch means and supplying coded impulse signals to said latch means, read-only memory character generating means coupled to the output of said input latch means, high voltage gates coupled to the output of said character generating means, variable delay means coupled to said input circuit means, bistable means coupled to the output of said variable delay means, variable rate astable means coupled to the output of said variable delay means, gating means responsive to the outputs of said astable and bistable means, a ring counter coupled to the output of said gating means, a plurality of column enable lines coupling said ring counter to said character generating means, said ring counter sequentially energizing said enable lines, a plurality of high voltage gates equal in number to said plurality of electrodes coupled to the output of said character generating means, said gates receiving signals responsive to coded signals supplied to said memory character generating means by said input data row lines, high voltage pulse supply means gated by said gating means, means coupling said high voltage supply means to said high voltage gates, circuit means for coupling the outputs of said high voltage gates to said electrodes in said printing head, circuit means for coupling said bistable means and said input latch means to said ring counter whereby said bistable means and said input latch means are reset at the termination of said counter sequence, and motor means coupled to said input circuit means for driving said belt and moving said recording sheet in response to said trigger pulse.
 2. The teleprinter of claim 1 further comprising switch means integral with said printing stylii head for controlling said motor so as to position said head.
 3. The teleprinter of claim 1 wherein said head comprises a plurality of insulated electrode fingers extending transversely from said head whereby said printing is visible as it is being printed.
 4. In an impactless, asynchronous teleprinter for printing characters in a matrix font including a printing stylii having a plurality of electrodes and movably carried by a belt transversely of a recording sheet, a printing control comprising input circuit means for receiving a trigger pulse, input data lines for supplying coded signals representing the character to be printed, character generating means coupled to said input data lines, gating means coupled to the output of said character generating means, bistable means coupled to said input circuit means, variable rate astable means coupled to said input circuit means, said bistable means and said variable rate astable means supplying a sequence of pulses in response to said trigger pulse, enabling means coupling said bistable means and said variable rate astable means to said character generating means, and circuit means for coupling said gating means to said input circuit means.
 5. The printing control of claim 4 further comprising variable delay means coupled between said input circuit means and said bistable means and said astable means. 